The present invention relates to a new and improved method of enlarging the width of a continuously cast strand, especially a steel strand, wherein at least a short or narrow side of an adjustable mold can be moved during the casting operation.
There has already become known to the art an accepted method wherein there is used a continuous casting mold having a short or narrow side which is divided into an upper part and a lower part. During change in the width of the cast strand the upper, non-imbued or non-wetted part is adjusted to a desired extent or position and the withdrawal of the steel strand as well as the oscillation device for the mold is stopped. The bath level in the mold ascends until arriving at the upper part of the mold. After there has been formed an adequate skin thickness at the casting or cast strand, during which the infeed of the melt to the mold at least must be throttled, the lower part is adjusted and the withdrawal of the cast strand can proceed.
Due to stopping the oscillatory motion of the continuous casting mold, it is necessary however to accept a repeated adhesion of the melt with the mold walls. A further drawback which is present with this state-of-the-art technique, resides in the fact that due to bringing the cast steel strand to standstill there is undesirably altered the cooling conditions, something which is unsatisfactory from the metallurgical standpoint, because then there no longer can be ensured for a constant quality of the cast strand over the entire strand length.
Apart from the foregoing, there is also known to the art a method wherein the small or narrow sides of the continuous casting mold are slowly completely retracted, without the need to interrupt the infeed of the melt to the continuous casting mold. Since, however, there can not be avoided the formation of a gap between the strand skin or shell and the small sides of the mold, it is not possible to positively eliminate bowing-out of the casting, and which phenomenon is associated with the danger of metal break-out, within a vertical section formed by the mold. Furthermore, the slow displacement requires an increased expenditure in time during adjustment of the mold, and therefore, a larger transition path, i.e., the region of the width change in the lengthwise direction of the cast strand.
The following numerical values given in the below-listed Table and derived from a conventional method, are useful for underscoring the correlation between the casting speed, displacement speed of the narrow or small side and the magnitude of the bowing-out or bulging of the casting:
______________________________________ Speed of Retraction of the Small Side of Degree of Casting Speed the Mold Bulging ______________________________________ 0.5 m/min 5 mm/min 1 - 2 mm 1.0 m/min 5 mm/min 10 - 15 mm 1.0 m/min 8 mm/min 15 - 20 mm ______________________________________